The Basics Of Blood :

15th Agust, 2002 ABO & Rh Isoimmunisation - Prof.S.N.Panda 3 The Basics Of Blood Controlled by genes at unknown No. of chromosomal loci.
Appearance by 40 days of I.U. Life- unchanged till death.
Also present in tissues & tissue fluids.
Blood group system: A group of antigens controlled by a locus having a variable no of allele genes. Antigens: -

The Basics Of Blood :

15th Agust, 2002 ABO & Rh Isoimmunisation - Prof.S.N.Panda 6 The Basics Of Blood Antibodies are formed against most of the major group antigens & present in almost all individuals when the antigen is absent.
In most other minor systems, natural antibodies to the antigens are found occassionally but as their anitgenicity is low, the immune antibodies are also rare ( except –Kell & Duffy)
Mostly of them are IgM type.
React poorly at body temp. ( except anti-A & anti-B), but agglutinate R.B.C.s at 5-20°C
Usually do not cross placenta. Natural Antibodies: -

ABO Blood Group System :

15th Agust, 2002 ABO & Rh Isoimmunisation - Prof.S.N.Panda 9 ABO Blood Group System ABO system is controlled by allelic genes A1, A2, B, O located on the long arm of chromosome 9
The loci of ABO & H are not genetically linked
A1 & A2 genes perform same function but have a different rate constant
The O gene is an amorph & functionaly silent
The H antigen is a precursor to A & B
Secretors & nonsecretors – Se & se genes control the production of a flucosyl transferase, which controls the production of H, A & B antigens in tissues

ABO System & Pregnancy :

15th Agust, 2002 ABO & Rh Isoimmunisation - Prof.S.N.Panda 12 ABO System & Pregnancy In foetus & newborn, RBCs have a decreased No. of H, A & B reactive sites
The foetal immunoglobulin production is low, so the plasma contains very little of anti-A & B agglutinins
Anti-A & B produced in the mother being natural are IgM molecules & so do not cross placenta.
In some type O adults, much of the anti-A & B and anti-AB (a cross reacting antibody, also called anti-C) isoagglutinins are of IgG class.

ABO System & Pregnancy :

15th Agust, 2002 ABO & Rh Isoimmunisation - Prof.S.N.Panda 13 ABO System & Pregnancy There is no adequate method of antenatal diagnosis.
Direct Coomb’s antiglobulin test may be negative in ABO haemolytic disease.
ABO haemolytic disease is frequently seen in infants of primigravidae & the chance of recurence is 87%.
The risk of stillbirth is not increased & no antenatal treatment is necessary.
Only 67% of affected infants will need any treatment.

Rhesus Blood Group System :

15th Agust, 2002 ABO & Rh Isoimmunisation - Prof.S.N.Panda 16 Rhesus Blood Group System 12 sets of combinations & 78 genotypes are possible. Most frequent genotypes are –
Cde/cde(33%), Cde/cDe(18%), Cde/cDE(12%) cDE/cde(11%), cde/cde(15%), cdE/cde(1%), Cde/cde(1%)
Though several Rh genotypes and phenotypes have been described, for clinical & all practical purposes it is enough to know whether one is Rh POSITIVE or NEGATIVE against anti D sera.

Rhesus Blood Group System :

15th Agust, 2002 ABO & Rh Isoimmunisation - Prof.S.N.Panda 17 Rhesus Blood Group System Incidence of Rh negative varies in different races:
Mongoloids- nil, Chinese & Japanese- 1-2%, Indians-5%, Africans-5-8%, Causcasians-15-17% & Basques-30-35%.
The antigenic expressions of these genes are dependent on an interaction between R.B.C. membrane protein & phospholipid molecules resulting in a set of antithelical epitopes, the coresponding antigens, consisting of C/c, D/d, E/e.
The antigenic determinants form an intrinsic part of the red cell membrane protein structure.

Rhesus Blood Group System :

15th Agust, 2002 ABO & Rh Isoimmunisation - Prof.S.N.Panda 18 Rhesus Blood Group System C/c & E/e are weak antigens and impractical to match.
‘D’ is by far the most immunogenic in the Rh system excepting those that have the natural antibodies.
There is a rare type of Rh negative called Rh null who lack all known Rh antigens.
‘D’ antigen has no natural antibody while C & E have the coresponding natural antibodies, though weak & found infrequently.

Pathogenesis Of Rh Iso-immunisation :

15th Agust, 2002 ABO & Rh Isoimmunisation - Prof.S.N.Panda 21 Pathogenesis Of Rh Iso-immunisation Chances of T.P.H/F.M.H. are only 5% in 1st trimester but 47% in 3rd trimester, many conditions can increase the risk.
Chances of primary sensitization during 1st pregnancy is only 1-2%, but 10 to 15% of patients may become sensitized after delivery.
ABO incompatibility and Rh non-responder status may protect.
Amount of antibodies that enter the fetal circulation will determine the degree of haemolysis